Device and method for simulating deep ground high temperature-three-dimensional ground stress coupling environment through prestressed steel strand

Abstract

The invention belongs to the technical field of deep ground environment mechanical testing, and discloses a device and method for simulating a deep ground high temperature-three-dimensional ground stress coupling environment through a prestressed steel strand. The device comprises a test piece main body system, a prestress applying system, a positioning reinforcing system and a monitoring feedback system. The core of the method is that based on a thermal stress formula under three-dimensional complete constraint in thermoelastic mechanics, additional thermal stress caused by ground temperature rise is calculated, and the additional thermal stress and target three-dimensional ground stress are superposed; and through a post-tensioning pre-stress technology, the superposed total stress is accurately and stably applied to an internal test piece for a long time by utilizing a retard-bonded pre-stress steel strand system and a high-strength concrete transfer medium, so that a deep high-ground-temperature and high-ground-stress coupled mechanical environment is constructed. The problems that a traditional coupling test device is high in cost, difficult to control and difficult to stabilize for a long time are solved, and accurate simulation of the deep ground high temperature-three-dimensional stress coupling environment is achieved.

Description

Technical Field

[0001] This invention belongs to the field of deep-earth environment mechanical testing technology, specifically, it relates to a device and method for simulating a deep-earth high-temperature-triaxial geostress coupling environment using prestressed steel strands. Background Technology

[0002] Deep rock masses exist in complex geological environments characterized by both high geostress and high geothermal temperatures. Increased temperature leads to thermal expansion of the rock mass, which, constrained by the surrounding rock mass, cannot deform freely, thus generating additional thermal stress on top of the original geostress. This temperature-stress coupling effect significantly impacts the mechanical properties, failure modes, and engineering stability of deep rock masses, making it a critical scientific issue that must be considered in deep resource development and underground engineering construction.

[0003] Currently, indoor simulations of such coupled environments primarily employ two technical approaches: one is to use conventional triaxial or true triaxial testing machines with temperature control, heating the specimen within a pressure chamber while simultaneously applying confining and axial pressures; the other is to construct large-scale physical models, simultaneously setting up loading and heating systems within or at the boundaries of the model. Both methods have significant limitations: the former involves complex and expensive equipment, small specimen sizes, and significant challenges in sealing and controlling under high temperature and pressure; the latter is costly, time-consuming, lacks flexibility, and struggles to achieve independent and precise control and long-term stability of the stress state. To address these issues, there is an urgent need for a device and method capable of accurately simulating the deep-earth high-temperature-triaxial geostress coupled environment. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a device and method for simulating a deep-earth high-temperature-triaxial geostress coupling environment using prestressed steel strands.

[0005] This method, based on the principles of thermoelasticity, theoretically calculates the additional thermal stress caused by deep geothermal temperatures and superimposes it with the original triaxial geostress to obtain the equivalent total stress. Then, using post-tensioning prestressing technology and high-strength concrete as the transfer medium, the prestress of the steel strands is uniformly applied to the internal target stress specimen, constructing a deep-earth high-temperature-triaxial geostress coupled environment. This method can solve the problems of stress instability and low scene reproduction in existing geostress simulation technologies, achieving precise application and independent control of triaxial geostress.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] 1. A device and method for simulating a deep-earth high-temperature-triaxial stress coupling environment using prestressed steel strands, comprising: a specimen main body system, a prestressing application system, a fixing and reinforcement system, and a monitoring and feedback system; wherein: the specimen main body system comprises, from the inside out, a target stress specimen and a high-strength concrete outer layer. The high-strength concrete outer layer bears the prestress of the steel strands, uniformly transferring the stress to the internal target stress specimen. The prestressing application system consists of loosely bonded steel strands, tensioning equipment, and anchors. The loosely bonded steel strands are equipped with anti-corrosion grease and a sheath, which can replace the duct forming and temporary protection functions of corrugated pipes, eliminating the need for additional corrugated pipes. The loosely bonded prestressed steel strands are independently arranged along the specimen in three directions: up / down, left / right, and front / back, achieving independent control of triaxial stress. The tensioning equipment is used to apply the pre-set prestress using the post-tensioning method, and the anchors are installed at both ends of the steel strands to fix the prestress and prevent stress attenuation. The fixing and reinforcement system consists of perforated templates and a grid of additional reinforcing bars. The template has precisely drilled holes according to the number and spacing of the steel strands to fix the positions of the loosely bonded steel strands before pouring concrete. Additional reinforcing bars are laid inside the high-strength concrete, arranged in conjunction with the steel strands, serving the dual purpose of preventing localized crushing of the concrete and secondary fixing of the steel strands. The monitoring and feedback system consists of resistance strain gauges and a data acquisition instrument. The resistance strain gauges are adhered to the surface of the target stress specimen; the data acquisition instrument is used to collect strain data from the target stress specimen, calculate prestress values, and realize data storage and analysis.

[0008] Compared with the prior art, the present invention has the following beneficial effects:

[0009] 1. Based on the thermoelastic mechanics formula, geothermal stress is accurately quantified and superimposed with the original geothermal stress. Then, it is applied through prestressed steel strands to realistically simulate the triaxial geothermal stress environment under the influence of geothermal stress in deep strata, with high scene reproduction.

[0010] 2. After the prestressed steel strands are fixed, their stress state remains stable over a long period of time, ensuring the long-term stability of the simulated triaxial stress field and the reliability of the test results.

[0011] 3. The device has a relatively flexible structure and can prepare simulated specimens of different sizes according to experimental requirements.

[0012] 4. The system structure has lower construction and operation costs than large hydraulic true triaxial systems, and the stress magnitude, direction and path can be flexibly adjusted. Attached image description:

[0013] Figure 1 This is a schematic diagram of a prestressed steel strand device for simulating a deep-earth high-temperature-triaxial geostress coupling environment.

[0014] Figure 2 This is a detailed schematic diagram of the tensioning end and the fixed end node of the prestressed tendon.

[0015] Figure 3 This is a schematic diagram of the overall specimen cross-section and the arrangement of resistance strain gauges.

[0016] Figure 4 This is a schematic diagram of the perforation template.

[0017] Figure 5 This is a schematic diagram of an additional steel reinforcement grid.

[0018] Figure 6 These are three views of the arrangement of prestressed steel strands.

[0019] In the figure: 1. Specimen main system, 2. Prestressing application system, 3. Fixing and reinforcement system, 4. Detection feedback system. Detailed implementation method:

[0020] like Figure 1 As shown, a device for simulating a deep-earth high-temperature-triaxial geostress coupling environment using prestressed steel strands includes: a specimen main body system 1, a prestressing application system 2, a fixing and reinforcement system 3, and a detection and feedback system 4; wherein: the prestressing application system 2 acts on the specimen main body system 1 to apply geostress of different directions and magnitudes to the entire specimen; the fixing and reinforcement system 3 realizes the casting and molding of the specimen main body system 1; the detection and feedback system 4 is connected to the surface of the stressed specimen through 41 resistance strain gauges to receive strain signals in real time, and the data acquisition instrument realizes data storage and analysis.

[0021] The main body system 1 of the specimen includes a target stress specimen 11 (taking a cylindrical specimen as an example) and a high-strength concrete outer layer 12, wherein: the high-strength concrete outer layer 12 bears the pre-compression stress of the steel strand and uniformly transfers the stress to the internal target stress specimen.

[0022] The prestressing application system 2 includes a loosely bonded prestressed steel strand 21, a hydraulic tensioning machine 22, a fixed-end compression anchor 23, an anchor plate 24, a spiral stirrup under the anchor 25, and a tensioning-end wedge anchor 26. The loosely bonded prestressed steel strand 21 is equipped with anti-corrosion grease and a sheath, which can replace the duct forming and temporary protection functions of corrugated pipes, eliminating the need for additional corrugated pipe installation and simplifying the construction process. The hydraulic tensioning machine 22 is used to apply pre-set prestress to the loosely bonded prestressed steel strand 21 using a post-tensioning method. The tensioning-end wedge anchor 26 is used to fix the tension of the steel strand. The anchor plate 24 bears the concentrated force and achieves stress diffusion, preventing local crushing. The spiral stirrup under the anchor 25 provides circumferential restraint to counteract splitting tensile stress. The fixed-end compression anchor 23 is pre-embedded in the non-tensioning end of the concrete, providing reliable reaction force for the tensioning operation.

[0023] The fixed reinforcement system 3 includes a perforated template 31 and a grid-reinforced steel bar 32. The template is precisely perforated according to the design quantity and spacing of the steel strands to ensure that each slow-bonded prestressed steel strand can be accurately positioned and fixed in the preset direction and position before concrete pouring. The grid-reinforced steel bar 32 is laid inside the high-strength concrete and is arranged in coordination with the steel strands. When under stress, it enhances the local compressive strength of the high-strength concrete and prevents crushing damage. During the construction stage, it forms a secondary positioning and constraint for the steel strands, effectively ensuring their spatial stability during the pouring and hardening process.

[0024] The detection feedback system 4 includes a resistance strain gauge 41 and a data acquisition instrument 42. The resistance strain gauge 41 is attached to the surface of the target stress specimen. The data acquisition instrument 42 is used to collect the strain data of the target stress specimen, calculate the prestress value, and realize the data storage and analysis.

[0025] The operation method of a device for simulating a deep-earth high-temperature-triaxial geostress coupling environment using prestressed steel strands is as follows:

[0026] (1) Calculate the additional thermal stress σ generated by deep-earth high temperature according to the formula of additional thermal stress under three-dimensional constraints. T And superimposed with the initial ground stress of the target (σ) x0 , σ y0 , σ z0 The equivalent total geostress value (σ) is obtained. x , σ y , σ z ).

[0027]

[0028] In the formula, α is the coefficient of thermal expansion of the target stress specimen, E is the elastic modulus of the target stress specimen, T is the temperature change, and ν is the Poisson's ratio of the target stress specimen.

[0029] (2) Based on the equivalent total ground stress, calculate the number of prestressed steel strands required in each direction, their spacing, and the tension force per strand. Design the perforation template accordingly, ensuring that the perforation positions on each side of the template are consistent with the design coordinates. Prepare components such as the steel reinforcement grid, anchor plates, anchor spiral stirrups, fixed-end extrusion anchors, and tension-end wedge anchors.

[0030] (3) At the fixed end of the specimen, install the extrusion anchor at the end of the prestressing tendon. Pass the prestressing tendon with the extrusion anchor through the corresponding hole in the template and use the template for end positioning. Tie a steel grid inside the template to provide auxiliary support and positioning for the middle section of the prestressing tendon, forming a preliminary spatial skeleton.

[0031] (4) At the tensioning end of the specimen, install the anchor plate tightly against the inside of the template and tie the spiral stirrup behind it. Pass the other end of the prestressing tendon through the area of ​​the anchor plate and spiral stirrup, in preparation for subsequent tensioning.

[0032] (5) Place the target stress specimen in the center of the template frame at the designed position and fix it. Select points on the surface of the target stress specimen and attach resistance strain gauges, lead out wires and connect them to the data acquisition instrument to complete the debugging of the monitoring system.

[0033] (6) Pour high-strength concrete in layers inside the formwork, vibrate to ensure compaction, and ensure that the prestressing tendons and internal specimens do not shift. After pouring, perform standard curing until the concrete reaches the design strength.

[0034] (7) Remove the lateral formwork. Install the tensioning end anchorage and hydraulic tensioning machine at the tensioning end. Perform post-tensioning on the prestressed tendons in each direction according to the design tension value. During the tensioning process, collect strain data in real time using a data acquisition instrument to monitor the strain response of the test specimen and verify the prestress transfer effect.

[0035] (8) After the prestressed steel strands in all directions are tensioned and anchored, the system is stabilized in a deep-earth high-temperature-triaxial geostress coupling environment. Stress and strain data are recorded by a data acquisition instrument throughout the test.

Claims

1. A device for simulating a deep-earth high-temperature-triaxial geostress coupling environment using prestressed steel strands, comprising: The system comprises a main specimen system, a prestressing application system, a fixing and reinforcement system, and a monitoring and feedback system. The main specimen system, from the inside out, consists of the target stress specimen and a high-strength concrete outer layer. The high-strength concrete outer layer bears the prestress of the steel strands and uniformly transfers the stress to the target stress specimen. The prestressing application system consists of loosely bonded steel strands, tensioning equipment, and anchors. The loosely bonded steel strands are evenly distributed along the specimen in three directions: vertical, horizontal, and front-back. The tensioning equipment applies the pre-set prestress using the post-tensioning method, and the anchors are installed at both ends of the steel strands to fix the prestress and prevent stress attenuation. The fixing and reinforcement system consists of perforated templates and a grid of additional reinforcing bars. The templates are pre-drilled according to the design to precisely position each steel strand. The grid of additional reinforcing bars is laid inside the high-strength concrete, working in conjunction with the steel strands to both prevent localized concrete crushing and provide secondary fixation for the steel strands. The monitoring and feedback system consists of resistance strain gauges and a data acquisition instrument. Resistance strain gauges are attached to the surface of the target stress specimen; a data acquisition instrument is used to collect strain data of the target stress specimen, calculate prestress values, and realize data storage and analysis. The operation method of the device used above to simulate the deep-earth high-temperature-triaxial geostress coupling environment using prestressed steel strands is as follows: (1) Calculate the additional thermal stress σ generated by deep-earth high temperature according to the formula of additional thermal stress under three-dimensional constraints. T And superimposed with the initial ground stress of the target (σ) x0 , σ y0 , σ z0 The equivalent total geostress value (σ) is obtained. x , σ y , σ z ). In the formula, α is the coefficient of thermal expansion of the target stress specimen, E is the elastic modulus of the target stress specimen, T is the temperature change, and ν is the Poisson's ratio of the target stress specimen. (2) Based on the equivalent total ground stress, calculate the number of prestressed steel strands required in each direction, their spacing, and the tension force per strand. Design the perforation template accordingly, ensuring that the perforation positions on each side of the template are consistent with the design coordinates. Prepare components such as the steel reinforcement grid, anchor plates, anchor spiral stirrups, fixed-end extrusion anchors, and tension-end wedge anchors. (3) At the fixed end of the specimen, install the extrusion anchor at the end of the prestressing tendon. Pass the prestressing tendon with the extrusion anchor through the corresponding hole in the template and use the template for end positioning. Tie a steel grid inside the template to provide auxiliary support and positioning for the middle section of the prestressing tendon, forming a preliminary spatial skeleton. (4) At the tensioning end of the specimen, install the anchor plate tightly against the inside of the template and tie the spiral stirrup behind it. Pass the other end of the prestressing tendon through the area of ​​the anchor plate and spiral stirrup, in preparation for subsequent tensioning. (5) Place the target stress specimen in the center of the template frame at the designed position and fix it. Select points on the surface of the target stress specimen and attach resistance strain gauges, lead out wires and connect them to the data acquisition instrument to complete the debugging of the monitoring system. (6) Pour high-strength concrete in layers inside the formwork, vibrate to ensure compaction, and ensure that the prestressing tendons and internal specimens do not shift. After pouring, perform standard curing until the concrete reaches the design strength. (7) Remove the lateral formwork. Install the tensioning end anchorage and hydraulic tensioning machine at the tensioning end. Perform post-tensioning on the prestressed tendons in each direction according to the design tension value. During the tensioning process, collect strain data in real time using a data acquisition instrument to monitor the strain response of the test specimen and verify the prestress transfer effect. (8) After the prestressed steel strands in all directions are tensioned and anchored, the system is stabilized in a deep-earth high-temperature-triaxial geostress coupling environment. Stress and strain data are recorded by a data acquisition instrument throughout the test.

2. The apparatus and method for simulating a deep-earth high-temperature-triaxial geostress coupling environment using prestressed steel strands according to claim 1, characterized in that: Based on the formula for additional thermal stress under three-dimensional constraints, the influence of high-temperature deep Earth is equivalent to additional thermal stress σ. T And superimposed with the initial ground stress of the target (σ) x0 , σ y0 , σ z0 The equivalent total geostress value (σ) is obtained. x , σ y , σ z ).

3. The apparatus and method for simulating a deep-earth high-temperature-triaxial geostress coupling environment using prestressed steel strands according to claim 1, characterized in that: The anchorages in the prestressing system include a fixed-end compression anchor, a tensioning-end wedge anchor, an anchor plate, and a spiral stirrup under the anchor. The compression anchor is embedded in the fixed end of the concrete to provide reaction force for tensioning. The wedge anchor is used to tension and lock the steel strands. The anchor plate receives and diffuses the concentrated force. The spiral stirrup provides circumferential restraint to prevent the high-strength concrete from splitting.

4. The apparatus and method for simulating a deep-earth high-temperature-triaxial geostress coupling environment using prestressed steel strands according to claim 1, characterized in that: The template is precisely perforated according to the design quantity and spacing of the steel strands to ensure that each steel strand is fixed in the preset direction and position; the additional reinforcing bars of the grid are arranged in coordination with the steel strands to perform secondary positioning and constraint of the steel strands during the construction stage.

5. The apparatus and method for simulating a deep-earth high-temperature-triaxial geostress coupling environment using prestressed steel strands according to claim 1, characterized in that: Slow-bonded prestressed steel strands come with their own anti-corrosion grease and sheath, which can replace the duct forming and temporary protection functions of corrugated pipes, eliminating the need for additional corrugated pipe installation; the slow-bonded prestressed steel strands are independently arranged in the three directions of the specimen (up, down, left, right, and front and back) to achieve independent control of three-dimensional stress.

6. The apparatus and method for simulating a deep-earth high-temperature-triaxial geostress coupling environment using prestressed steel strands according to claim 1, characterized in that: The high-strength concrete outer layer bears the pre-compression stress of the steel strands, and uniformly transfers the stress to the target stress specimen.

7. The apparatus and method for simulating a deep-earth high-temperature-triaxial geostress coupling environment using prestressed steel strands according to claim 1, characterized in that: The monitoring and feedback system includes resistance strain gauges and a data acquisition instrument to collect and store stress and strain data during the experiment.

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